In order to increase the rate of working in conventional hammers, it is known to provide a resilient return arrangement provided to act upon the reciprocating tool member to accelerate its return movement after a working stroke producing the hammer impact. Thus, in previous designs of diesel-powered hammers, the diesel piston has had its upper end moving in a closed cylinder that thereby acts as an air spring when the air within it is compressed with the upward movement of the piston.

Although such an accelerated return of the piston can produce a marked increase in the cycle frequency it is possible, and is especially apparent in general in diesel-powered hammers, that reaction forces of the resilient return means tend to lift the hammer, which is to be avoided, and when the hammer is arranged to act downwardly, as in a pile driver, it is usually necessary to make the cylinder construction relatively massive in order to prevent this from occurring.

According to the present invention, in a poweroperated hammer comprising a piston reciprocable to produce a series of working impacts, the piston projects into an enclosure that forms, with the surface of a part of the piston, a sealed space the volume of which increases with the return movement of the piston from a working impact, the arrangement being such that a suction force is developed that acts upon the said part of the piston surface in the opposite direction to said return movement.

It is found that, by using such an arrangement, the peak pressure force acting to accelerate the return motion of the piston is significantly reduced, since it is limited by the value of atmospheric pressure if the space beyond the piston is freely open to atmosphere, and in a hammer arranged for downwards driving the tendency to lift the hammer cylinder is correspondingly reduced. At the same time, the suction force is built up relatively quickly as the piston rises so that despite the reduction in peak force a similar increase of cycle frequency can be achieved as when using a compression air spring.

Preferably the piston is mounted in a casing comprising a first portion providing a space for pressure fluid to generate the working impacts, and a second portion in which said enclosed space is formed. Conveniently said first and second casing portions have different diameters, the piston being a unitary member having different diameter portions closely fitting the respective casing portions, when it can be arranged that the smaller diameter portions of the casing and piston cooperate to provide said working fluid space and the piston smaller diameter portion projects into the casing larger diameter portion whereby said sealed space is formed in an annular region therebetween and is closed by the piston larger diameter portion.

Advantageously, means are provided to open the sealed space to atmosphere at or near the beginning of said return movement of the piston, or relief valve means are provided to limit the pressure in said sealed space. Such a provision can prevent the generation of any significant positive gauge pressure in that space as the piston reaches the bottom of its stroke if there has been any leakage into the space while the piston was in a higher position and while a negative gauge pressure prevailed in the space.

By way of example only, a diesel-powered hammer according to the invention will now be described in greater detail with reference to the accompanying drawings of which:

FIG. 1 is a side view, in vertical section, of the lower region of the hammer, and

FIGS. 2 and 3 are side views, in vertical section of two alternative arrangements of the upper region of the hammer of FIG. 1.

Referring to the drawings, the hammer casing comprises a lower, cylindrical portion 2 and an upper, larger diameter cylindrical portion 4 secured to it. Slidably mounted in the lower end of the portion 4 and sealing that end is an anvil block 6. A piston 8 is reciprocable within the casing from a lowermost position illustrated in FIG. 1 by a compression ignition cycle being operated in the combustion space between the bottom of the piston and the casing portion 2. The piston 8, which may be of cast iron, has an integrally formed impact stem 10 slidable in and sealing with the portion 2 of casing, and an enlarged diameter head 12 located in. and sealing with the portion 4 of the casing. Secured to the lower end of the hammer casing are pile grips 14, to attach a pile P and hammer together with a pile dolly 16 sandwiched between the anvil block 6 and the pile.

The upper face of the anvil block 6 and the lower face of the piston stem 10 have opposed central cavities 18 while the outer region of these faces have complementary profiles sloping downwards towards the central cavities. Fuel is injected from a pump in a casing 20 on to the anvil sloping face, the fuel following the trajectory 22. The supply to the pump is from a fuel tank 24 on the upper portion 4 of the casing.

The fuel pump is operated with the reciprocation of the piston 8 by a cam 26 having spaced pivot connections to the casing lower portion and to rod 28 carrying a piston of the pump. The cam is spring-loaded to project through a slot 30 in the casing wall and bear against the piston stem 10. As the piston stem rises clear the slot, the cam moves inwards to draw fuel into the pump and when the piston stem next descends, it strikes the curved face of the cam and so displaces the rod 28 to inject thefuel through the line 22 into the combustion space. The injection is at low pressure since at this stage exhaust ports 34 (only one of which is shown) are not yet covered by the piston stem 10.

The piston head 12 forms, with a. spring sealing ring 36 located at the junction between the upper and lower casing portions, an enclosed space 38 that is joined to the space above the piston, when the piston is in its lowermost position, by a channel 40, the function of which will be described below.

, The top end of the casing portion 4 is open to atmosphere. Each time the piston 8 rises after ignition of fuel injected with the casing below it, the space 38 is sealed off once the piston head 12 has covered the upper end of the channel 40, and further upwards movement of the piston then increases the volume of the space 38 below the piston, with a consequent reduction in pressure within this space. Hence, as a result of the fact that the space is substantially sealed from its surroundings during at least a major portion of its increase in volume, a suction effect is set up on the base of the piston head 12 which tends to reduce the rise in the piston, the suction force increasing as the volume of the space 38 increases with the rise of the piston. The maximum suction pressure is of course dictated by atmospheric pressure so that the maximum reactive force lifting the casing is always less than that due to atmospheric pressure on the flange 2a of the portion 2 of the casing below the sealing ring.

Once the piston begins its downwards compression stroke the gravitational force on the ram is supplemented by the downward suction force in the increased volume of the space 38, and the ram is accordingly accelerated by both forces, the latter force decreasing with decrease in volume of the space 38.

Since there can be expected to be some leakage of air into the space 38 while it is held at a negative gauge pressure, the pressure in the space would, without the channel 40, exceed atmospheric by a small amount at the end of he downward stroke. By interconnecting the space 38 through the channel 40 with the open upper end of the casing as the piston nears the bottom of its stroke, it is possible to ensure that this pressure is never in fact greater than atmospheric. An alternative way of achieving this effect would be to connect the bottom of the space 38 directly to atmosphere through a nonreturn relief valve (as indicated at 42 in FIG. 3) arranged to open when the internal pressure exceeds atmospheric.

In order to start the operation of the hammer, in the arrangement illustrated in FIG. 2, the piston 8 has a central cylindrical bore 44 into which projects a rod 46 carrying a terminal enlargement 48. The rod 46 extends the length of the portion 4 of the casing and has attached to its other end a suspension eye 50. The upper end of the bore 2 has a tubular plug 52 of diameter less than that of the enlargement 48 so that an abutment surface is presented to the enlargement when the rod 46 is raised and the piston 8 can thus be lifted to an uppermost position and then allowed to drop to start operation of the hammer.

An alternative starting arrangement shown in FIG. 3 employs a similar piston with a plug 52 secured to the upper end of its bore. A tube 54 is fixed to the top of the casing in this case and is a free sliding fit in the plug 52. A rod 56 with a suspension eye 58 attached to its upper end has an engagement linkage at its lower end comprising an abutment member 60 pivoted to the rod and joined to a hook member 62 by a pivot link 64. Both the abutment and hook members project through an elongate slot 66 in the tube 54. When the rod is lifted by the suspension eye, the member 60 engages the plug and the piston is then drawn up with the rod. The width of the slot is reduced in its upper region and the hook member 62 is made rather wider than the abutment member 60 so that as it reaches this region it is restrained and is pivoted inwards, the connecting link 64 being drawn downwards thereby to pivot the engagement member inwards also. As a result, the piston plug is no longer held by the engagement element and the piston is allowed to fall. The mechanism is reset to the illustrated position by lowering the rod 56 until the hook member 62 abuts pin 68, the weight of the rod then urging the engagement and hook members outwards and swinging the link 64 back past its overcenter position.

This alternative arrangement has the advantage that it is not necessary to lift the piston with a winch that has a free-fall pay-out mechanism since the rod 56 need not fall with the piston.

In order to lubricate the hammer, the casing containing the fuel pump has a separate cylinder space for the pumping of lubricating fluid, this flow being actuated by a further shoulder or piston head on the same piston rod 28. From the lubricating pump oil is directed, firstly, into the upper casing portion 4 for lubrication of the rings of the piston head 12, secondly into the lower casing portion 2 for lubrication of the rings of the piston stem 10, and thirdly to the outer circumference of the anvil block 6 for lubrication of this block in its sliding contact with the casing.

While only a diesel-powered hammer has been illustrated in the foregoing description it will be understood that the invention can be applied to hammers having other driving means, for example, compressed air, in an entirely analogous manner and no further description is therefore necessary. It will also be apparent that the invention can be applied to hammers arranged for operations other than pile-driving, as for example rock breaking.

What we claim and desire to secure by Letters Patent l. A power-operated hammer comprising, in combination, a casing, a piston reciprocable in the casing to produce a series of working impacts, an enclosure formed between the casing and a projecting part of the piston, said enclosure being partly bounded by the surface of a part of the piston to define an enclosed space the volume of which increases with the return movement of the piston from a working impact, the enclosed space being substantially sealed from its surroundings during at least a major portion of its increase in volume such that a suction force is developed during such portion of its increase in volume that acts upon the said part of the piston surface in the opposite direction to said return movement.

2. A hammer according to claim 1 wherein means are provided to open the enclosed space to atmosphere at or near the beginning of said return movement of the piston.

3. A hammer according to claim 1 wherein relief valve means are provided to limit the pressure in said enclosed space.

4. A hammer according to claim 1 wherein the casing comprises a first portion providing a space for pressure fluid to generate the working impacts, and a second portion in which said enclosed space is formed.

5. A hammer according to claim 4 wherein said first and second casing portions have different diameters, different diameter portions of a unitary piston closely fitting the respective casing portions.

6. A hammer according to claim 5 wherein the smaller diameter portions of the casing and piston cooperate to provide said working fluid space and the piston smaller diameter portion projects into the casing larger diameter portion whereby said enclosed space is formed in an annular region therebetween and is closed by the piston larger diameter portion.

7. A hammer according to claim 6 further comprising means in said second casing portion arranged to bring the regions on opposite sides of the larger diameter piston portion in communication with each other at or near the beginning of said return movement of the piston.

8. A hammer according to claim 1 arranged for diesel operation, a working fluid space between the casing and the piston forming a combustion chamber and being disposed in a lower region of the hammer, a member underneath the hammer being arranged to receive the working impacts.

9. A hammer according to claim 8 wherein a hollow core is provided in the piston, lifting means being in sertable into said hollow core to engage and lift the piston for starting operation of the hammer.

10. A hammer according to claim 9 wherein the lifting means comprises a suspended engagement element, a restriction at the upper end of said core being engageable with said element to allow the piston to be lifted therewith.

11. A hammer according to claim 10 wherein means are provided to retract said engagement element at a predetermined raised position of the piston to release the piston and allow it to fall.

12. A diesel-powered hammer comprising, in combination, a casing having a cylindrical lower portion providing the combustion space and a larger cross-section upper portion, a piston reciprocable in the casing having a lower portion forming an upper boundary of the combustion space, an enlarged head of the piston sealingly fitting said casing upper portion and defining therewith an enclosed space, an underface of said pis ton head forming an upper boundary of said enclosed space, the volume of said enclosed space increasing with the increase of volume of the combustion space, the enclosed space being substantially sealed from its surroundings during at least a major portion of its increase in volume such that, as the piston rises in the casing, a suction force is developed acting on said underface to accelerate the return of the piston in a downwards working stroke.